New Horizons set to write the book on PlutoAlmost ten years after it launched, NASA's New Horizons spacecraft is closing in on Pluto.

USA TODAY By James Dean, Florida Today | July 12, 2015, 6:39 PM EDT

CAPE CANAVERAL - At the risk of an upset stomach, Chuck Tatro plans to make good on a nearly decade-old promise Tuesday.

As part of the Kennedy Space Center team that helped ready the New Horizons mission for launch from Cape Canaveral in January 2006, Tatro on launch day received a small bag of blue, mission-themed M&Ms from the spacecraft builders.

"I said, 'I'm going to keep those on my desk and I'm going to open those M&Ms and eat them when you arrive at Pluto,'" Tatro remembers.

That day has finally come with the New Horizons probe, after a nine-and-a-half-year journey spanning more than 3 billion miles, set to zip close past Pluto and its five known moons at 7:49 a.m. ET Tuesday.

[...]New Horizons passed the moon in nine hours, 10 times faster than an Apollo mission. It flew by the orbit of Mars in less than three months and past Jupiter in just 13 months -- the only planet to provide a gravity assist along the way.

The spacecraft spent much of the mission in hibernation, until a final wake-up call in December set the stage for a months-long approach that has produced increasingly detailed images as New Horizons closes in on Pluto.

Flying at 31,000 mph, Tuesday's flyby will last just about 30 minutes as the spacecraft speeds through a narrow target zone. After more than nine years, the timing can't be off by much more than a minute.

When did the mission begin?New Horizons blasted off in January 19 2006, and was the fastest launch recorded, reaching speeds of over 36,000 miles per hour. The spacecraft passed the Moon after just nine hours, around eight times quicker than the Apollo programme, and reached Jupiter the following year.

What have we learnt in the past 24 hours?The new up-close images show that Pluto is slightly larger than we thought -2,370 kilometres (1,473 miles) in diameter - making it undisputedly the largest dwarf planet in the solar system. For the past decade astronomers had been undecided about whether Pluto or Eris, another dwarf planet beyond Neptune, was bigger. Astronomers already have good estimates of Pluto’s mass, and so the larger volume than expected means that Pluto must be less dense than we thought and probably contains more ice beneath the surface. Sensors on New Horizons also detected a thin nitrogen atmosphere extending far out into space, which scientists believe may shed snow, with nitrogen flakes tumbling down to the surface before evaporating again at the surface.

On Wednesday at around 3pm ET/ 8pm BST we are expecting a new set of images to be published from the moment of closest contact.[...]Where is New Horizons heading next?The mission is now speeding onwards into the Kuiper Belt where it will examine one or two of the ancient, icy miniature worlds in the vast region. The so-called Kuiper Belt Objects (KBOs) that it might fly-by include Quoar, Eris (close in size to Pluto), Makemake, Haumea or Sedna. In coming months, scientists will decide the spacecraft’s next target and send signals from Earth to New Horizons to thrust its rockets to tweak its trajectory.

When will the mission end?The fuel is designed to last until the late 2020s or even beyond. When it runs out of power, astronomers will lose contact with the probe and it will continue to drift out past the Kuiper belt and eventually leave the solar system.